1. Field of the Invention
This invention relates to catheters, and in particular, to a guiding catheter to be used in the performance of a percutaneous translumenal coronary angioplasty procedure, a guiding catheter which provides variable, operator-controlled flexibility. This feature facilitates introduction and precludes disengagement of the guiding catheter, thus expediting the performance, and enhancing the safety, of the angioplasty procedure.
2. Description of the Prior Art
In 1977 Andreas Gruntzig first used a balloon-tipped flexible catheter to percutaneously dilate a region of stenosis within the coronary artery of a patient with atherosclerotic coronary artery disease. Since that time, the incidence of percutaneous translumenal coronary angioplasty has increased exponentially. In the last several years, the performance of this procedure has become routine within most major medical centers throughout the world. Furthermore, with the advent of improved technology and increased operator skill, the indications for this procedure have also substantially increased. Concurrent with the aggressive utilization of this technique, physicians with expertise in angioplasty have been approaching increasingly difficult lesions percutaneously, and physicians with relatively little experience in angioplasty have been attempting to dilate relatively straight forward lesions with minimal formal training.
In a routine angioplasty procedure using conventional catheters, a preshaped semi-rigid guiding catheter is introduced into a peripheral artery, advanced over a guidewire along the course of the aorta and subsequently engaged within the appropriate coronary ostium. Once engaged, a second catheter (an angioplasty balloon dilation catheter), equipped with a balloon at its distal aspect and a flexible steerable guidewire, is introduced within the guiding catheter and advanced to within its distal aspect. The guidewire is then advanced within the lumen of the diseased vessel and manipulated across the region of stenosis. By rotating the guidewire, which contains a slight bend, the operator can control the course of the wire and select the appropriate lumen. Once the guidewire is positioned across the region of stenosis, the operator advances the dilation balloon over the guidewire and positions it across the stenotic lesion. The angioplasty is then accomplished by inflating the balloon to about 6-10 atmospheres of pressure. Usually three to four dilations are required for each region of stenosis, with the duration of each dilation varying between 30 to 90 seconds, depending upon anatomic considerations and operator preference. Following the final dilation, the guidewire and angioplasty balloon are withdrawn, leaving the guiding catheter in place. Coronary angiography may then be performed to evaluate the appearance of the vessel following the procedure and to determine the severity of any residual stenosis.
There are several major obstacles to the successful performance of the procedure. One major difficulty involves manipulation of the dilation balloon catheter across the region of stenosis within the appropriate coronary artery. Although the guidewire can frequently be advanced across the region with relative ease, manipulation of the balloon across the stenosis is more difficult because the catheter is substantially larger in cross section than the guidewire. Hence, relatively more resistance to the passage of this catheter within the coronary artery is commonly incurred. Merely advancing the angioplasty dilation balloon catheter against resistance often results in disengagement of the guiding catheter from the coronary ostium. Once the disengagement occurs, the angioplasty dilation balloon catheter frequently prolapses in the ascending aorta, precluding further advancement of this catheter. Inability to advance the angioplasty balloon across the stenosis because of instability of the guiding catheter and subsequent prolapse of the angioplasty balloon catheter represents one of the most common reasons for failure during the performance of a coronary angioplasty procedure. The guiding catheter disengages in this circumstance because of its flexibility. The guiding catheter has intrinsic flexibility because it must conform to the configuration of the aorta and aortic arch, which contain both linear and curved segments, during introduction. Insertion of the guiding catheter requires that it be advanced over a guidewire up the aorta, which is relatively straight, and then over the aortic arch.
One prior art solution to this difficulty was the manufacture of dilation balloon catheters designed to produce less resistance during manipulation across a stenotic lesion. It was originally proposed that these "low resistance" angioplasty dilation catheters would produce less "back pressure" and in this way preclude disengagement of the guiding catheter. Several approaches were pursued to minimize the resistance characteristics of the balloon catheters including the development of lower profile balloons (when deflated) with smooth, tapered leading edges. By itself, however, this approach did not circumvent the problem. For example, despite extensive research and development, the cross-sectional diameter of the lowest profile dilation catheter currently available is considerably greater than the corresponding diameter of the guide wires used in conventional coronary angioplasty. Hence, despite the development of these low profile dilation catheters, intracoronary resistance to the passage of these catheters remains a considerable problem. Secondly, these smaller catheters do not permit reliable transmission of intracoronary pressures and, for this reason, their use obscures vital hemodynamic monitoring on frequent occasions. And thirdly, the caliber of these low profile balloons, when inflated, is substantially smaller than the corresponding caliber of most conventional angioplasty catheters. Thus, their use frequently necessitates the installation of an intracoronary exchange wire as well as the introduction of a second (larger caliber) angioplasty dilation balloon catheter. The use of this second dilation catheter, and the necessary exchange wire, increases the time and expense of the procedure. Most significantly, the complication rate of the procedure increases as the time for, and number of, dilation balloon changes increases.
In the prior art, dislodgment of the guiding catheter was prevented by forcing the guiding catheter down the course of the vessel to be dilated or bending the guiding catheter in such a way that it "banked" off the back wall of the aorta before engaging the coronary ostium. Both techniques are particularly dangerous as they may result in dissection of the coronary artery proximal the region to be dilated.